Motion in a Straight Line

Question

A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15ms-¹. How long does the body take to stop?

Answer 1

Force : F=50N ; Mass : m=20kg ; Initial velocity : u=15m/s

From newton’s second law, F=ma

50=20×a

a=2.5m/s²

From equations of motion , v=u+at

 0 =15+(−2.5)t

Solve to get : t = 6s

Hence, the body will be stop in 6 seconds

Answer 2

F= 50N

m = 20Kg

therefore , a= F/m = 50/20 = 2.5

using v = u + at

0= 15 - 2.5(t)

t= 6sec.